The present invention relates to a solidification processing method, as well as a solidification processing apparatus, suitable for, with thermoplastics as a binder, manufacturing solid fuels usable as an alternative to fossil fuels such as coal and coke from waste plastics, waste paper, waste wood and the like that are hard to treat for material recycle in the industrial waste treatment.
Recycling process of wastes is important as a countermeasure against environmental problems. An example of practicalized recycling process of wastes is that flammable wastes including paper materials, plastic materials and cloth materials, such as shredder dust, food packaging containers or used clothes are utilized as raw materials of regenerated fuels.
As an apparatus for manufacturing solid regenerated fuels by using those kinds of wastes, a twin-screw extrusion molding machine as shown in FIG. 8 is conventionally known (see, e.g., JP H10-85701 A). This extrusion molding machine has, within a casing 101, a cylindrical-shaped hollow portion having a calabash-shaped cross section. Two screw shafts 103, 103 with their center axes directed parallel to each other are inserted in the hollow portion of the casing 101. Each of the screw shafts 103 has screw blades while a wingless increased-diameter portion 120 having no screw blades is formed so as to be shifted toward the forward end from a longitudinal center of the screw shaft 103. The screw shaft 103 has first screw blades 121 on one side closer to its base end than the wingless increased-diameter portion 120, and second screw blades 122 on one side closer its forward end than the wingless increased-diameter portion 120. An inner wall of the casing 101 that defines the hollow portion is proximate to outer edges of the first and second screw blades 121, 122 as well as proximate to a circumferential surface of the wingless increased-diameter portion 120 to form a restricting portion. The screw shafts 103 are driven by an unshown motor so as to be rotated in mutually opposite directions via mutually meshed gear wheels 111, 111. Thus, the first and second screw blades 121, 122 are driven into rotation so as to mesh with each other from up to down.
This twin-screw extrusion molding machine operates in the following manner. Wastes including waste plastic materials are preliminarily course crushed, selected, and inputted into the hollow portion through an input port 102 of the casing. The inputted wastes are, while crushed and kneaded, transferred to the wingless increased-diameter portion 120 side by the first screw blades 121 of the screw shafts. Heaters are provided on a side face of the casing 101 so that plastics in the wastes are softened or melted by heat of the heaters. Wastes containing the softened or molten plastics are compacted during a process of being extruded through between the restricting portion of the inner wall of the casing 101 and the wingless increased-diameter portion 120, thus being put into a fluidized state. The fluidized wastes are extruded in a bar-like form through nozzle holes 116 of an end face plate 115 by the second screw blades 122. The wastes extruded in the bar-like form are solidified as their temperature falls, thus solid regenerated fuels being obtained.
However, in this twin-screw extrusion molding machine, waste passages formed between the inner wall of the casing 101 and surfaces of the screw shafts 103 have cross sections decreasing from the first screw blades 121 toward the wingless increased-diameter portion 120 and increasing from the wingless increased-diameter portion 120 toward the second screw blades 122. Therefore, the wastes extruded through between the restricting portion of the inner wall of the casing 101 and the wingless increased-diameter portion 120 tend to be diffused between the inner wall of the casing 101 and the second screw blades 122. As a result, the wastes extruded through the nozzle holes 116 are relatively lower in density, posing an issue that the wastes tend to be insufficient in shape retention after the solidification.
Also, heating is applied over wide ranges within the casing 101 by the heaters provided on the side face of the casing 101, incurring problems of lower heating efficiency and lower precision of temperature control over the wastes. Lower precision of temperature control over the wastes may lead to high temperatures of the wastes, causing occurrence of inflammation or toxic gas, or otherwise lead to low temperatures of the wastes and to insufficient melting of the melting materials, incurring such disadvantages as insufficient shape retention of the solidified materials. These and other issues relating to the temperature control on the wastes are not taken into consideration in JP H10-85701 A.
Thus, in view of the issues of the above-described apparatus, there has been proposed an extrusion apparatus which is simple in structure and miniaturizable in size and yet generally equivalent or higher to conventional counterparts in terms of the power of breakage, kneading, melting and compaction, thus being suitable for manufacture of solid fuels from wastes (see, e.g., JP 2002-361492 A). However, in this apparatus, since the breakage, kneading, melting and compaction processes are rapidly performed due to its smaller size, there may result insufficient kneading of processed materials, or occurrence of inflammation due to abrupt temperature elevations of the processed materials.